Telephone trunking system.



il D, Fl. LES.

Patented June l?, 19H5.

connect ion UNITED sTArasrATENT OFFICE.

EDWARD D. FALES, 0F LA GRANGE, ILLINOIS, ASSIGNOR T0 AUTOMATIC ELECTRIC COMPANY, OF CHICAGO, ILLINOS, A CORPORATION 0F ILLINOIS.

TELEPHONE TRUNKING SYSTEM.

Application tiled July 6, 1908.

Sp'eciication of Letters Patent.

Patented June 17, 1918.

Serial No. 442.198.

` To all whom it muy conf'crn.'

, ing between two automatic exchanges, al- 15 though in certain respects. as will hereinafter appear, my invention is not limited to either a two-way or a one-way trunk.

My invention contemplates a two-way trunk-line provided with a non-numerical trunking switch at each end thereof, whereb v the scizurfl of either cud of said trunkline serves autou'iatically to operate a nonnumerical trunking switch at thc other end thereof, and to thus automatically extend therefrom to an idle switch, such, for example, as a selector' or connector, according to the size and character of the exchange.

My invention turthcr contemplates the provision of a two-way trunk in a twowire automatic telephone exchange systemer-that is to say, in a system in which the subscribers control or operate the automatic switches over complete metallic liucI circuits, rather than by means of a ground at the calling sllbstation.

lt also contemplates a twowvire system in which nonuiumerical trunkingl switches are provided for extending connection from trunk-lines to other trunk-lines, such nonnumcrical trunking switches being prefer ably interposed between numerical switches, as, for example, between the first and second selectors of a ten thousand or even larger exchange.

My invention contemplates, furthermore, a system in which 'certain switches can he tested and operated manually or forcibly to seize one end of a trunk-line, as is often necessary Ain the inspection of the central station apparatus, without making the other end of the two-way trunk busy, and whereby any switch operated in this way to seize a two-Way trunk can be forcibly or manually released therefrom without danger of leaving the other end of the trunk in a busy condition-that is to say, without danger of leaving it subject to such a vguarding potential as would prevent seizure thereof by subscribers attempting to call overthe trunk in the opposite direction.

In addition it contemplates certain details and combinations and features of improvement tending to increase the general etliciency ot' a telephone exchange system, as will hereinafter more fully appear.

ln the accompanying drawings Figures 1, 2 and 3 are a diagrammatical representation of a circuit connection established between a calling subscriber in Fig. 1 from one exchange, and a called subscriber i Fig. 3 at a second exchange, the said connection being established over a tivo-wav trunk of the circuit connection aforesaid.

The exchange in which the calling subscriber, shown in Fig` 1, is located is desig nated as exchange A or group A. This exchange or group is provided with a cen tralized battery B having, preferably, a grounded terminal G. This battery may be used for supplying all talking and operating` current to the exchange A. 0f the a paratus allotted to the exchange A, tllie drawings show the callin subscribers station C, the line switch lg allotted to said substation and individual to said substation C, but controlled, together with a number ot' other similar line switches, by the common mechanism E usually known as the master switch. Accessible to the line switch D is the numerical switch F, usually known as the first-selector, which is one of a group of selectors common to a number of line switches D greater in number than the number of selectors F in the group. The line, switches D which have access to the group of selectors aforesaid may be divided in one or more groups, and may be controlled by one or more master switches E. This arrangement., however, is not necessary, as there may be only one group of line switches D controlled by one master switch E, the total number of which line switches may be much greater than the total number of selectors F. Through the medium ot the selectors F the two-way trunks of my invention. such as the twoway trunk H, may be reached from thc A exchange, as, for example, by the subscriber C, as indicated in the drawings. The selectors F may 0r may not have access solely to two-way trunks H. The arrangement may be such, however, that the selector F will have access to trunks H from certain levels, while from other levels switches such as second-selectors or connectors, or selectors and connectors, may be reached. It will be seen that the twowvay trunk H terminates in the A exchange in a line switch I to the left of which are shown conductors in a trunk-line which may terminate in a connector switch or in a selector switch. The exchange in which the called subscriber J is located is designated as the A1 exchange. Of the A1 exchange apparatus the drawings show in addition to the called substation the called Subscriber-s line'switch D1, which is the same as the line switch D; a first-selector switch F1, which is the same as the selector switch F; a connector switch K and a second-selector L; and the line switch M is Shown, which is the A1 exchange termi nal of the two-way trunk H. In the A1 exchange there is shown another battery B1 having, preferably, a rounded terminal G1. This battery may e used for supplying all talking and operating current to the A1 exchange. It 1s not absolutely essential that these separate exchanges shall be supplied with current from separate batteries, inasmuch as the batteries B and B1 may be one and the same battery. It is to be understood that in the usual arrangement a line switch D (Fig. l) is provided with ten trunks, each a duplicate of the single trunk indicated, and each terminating in a selector switch F as does the trunk shown. It is to be understood also that in the usual arrangement each of these trunks is made common to all of the line switches of the same group, and it is obvious, therefore, that although the trunk 1 ruiming from the selector F to the line switch ,D is shown with only one lineswitch bank-terminal, this trunk is in reality provided with as many terminals as there are line-switch banks-that is, as many terminals as there are line switches. In like manner the trunk Il is shown with only one bank terminal in the selector F that is, it is to be understood that there are as many multiples of these terminals as there are selectorsl to which the trunk H is common. Likewise the A1 exchange twoway trunk line switch M is provided with ten trunks, each terminating in a secondselector L, and the selector F has access to the two-way trunks ll just as the selector F in Fig. l has aci-oss to the .said trunks ll: and similarly` the second-selector L has access to a n timber ol' connectors K. lt will be seen that the two-wafy trunk to the left of the dotted line in Fig. 2 is an exact du'- plicatc of that section of the two-way ti'unk to the right thereof.

Conciselv stated, the general method of operation is as follows: When a subscriber C (Fig. l) calls a subscriber J 3) the subscriber C removes-the receiver and thus operates his line switch D to establish connection with the selector F. The selector F is then operated by the subscriber upon the first move of the dial, by which operation the wipers are raised to a certain bank level along which they automatically rotate to piek out the first idle two-way trunk H available. As soon as the selector F stops on the trunk and connects the calling subscriber therewith, the line switch I is cut off from the trunk while the line switch M is operated to establish connection with the second-selector L. Of course, the selector F makes the tlunk H bilsy at the A exchange to all other switches to which the said trunk is accessible from that exchange. At the A1 exchange the` operation of the line switch M makes the trunk busy to all switches which have access to the trunk H at said exchange. `lt will be understood that by this operation the trunk is made instantly busy at both ends. 'hen the line switch M establishes connection with the selector L it cuts itself off from the trunk, thus giving the calling subscriber C a clear line from the A exchange to the A1 exchange. By the second operation of the dial the calling subscriber operates the second- Selector L, which latter operates in a similar manner to the selector F to [ind the connector K. The said connector now, as is usually the case, responds to the last two operations at the calling subscriber`s telephone. and in this manner the calling and called subscribers are placed in connection. After connection is established, as soon as the calling subscriber hangs up his receiver all of the switches are restored.I It will be seen that when a call passes from the A1 exchange to the A exchange, as. for example, when the subscriber J calls the subscriber C, then the order of operation is exactly reversed. First the line switch D operates to connect with the selector F1, which in turn responds to the first operation of the dial at the station and finds the twoway trunk H. s soon as connectionis established with the said trunk the line switch )l is eut oli" from the trunk, while the line |.switch l is caused to operate to establishy connection with a suitable switch, such as a selector l, and from thereon the operation of the selector and of the connector is the saine as previously explained.

Having thus outlined the general mode of operation, a somewhat detailed description nl' the apparatus is as follows: As shown at C (.Fig. l) the telephone is provided with the usual transmitter '2, induction-coil 3, re

'Ll-2. the vertical magnet. 43, the rotary mag v1n this case, connn'iscs the wipers 10.3. L10, 50,

'ceivei" 4, switch-hook Sand ringer 6. 1n addition ity isprovided with the usual calling mechanism comprisingr the impulse wheel 7 having on'its eriphery the impulse teeth 8 for operating tie impulse springs 0 and 10. The said impulse wheel 7 is, of course, dmounted on the saine shaft 11 the dial, .being rigid with the saine. Normally--that is, when the switch-hoek is down-the bell 6 is bridged across the line conductors 12 and 13 through the condenser 14. The line switch D is a modified forni of the line switch disclosed in British patent to A. E; Keith No. 26,301 of 1906, and in,the West em Electrician of Chicago, Illinois, of. January 25, 1908. As herein represented the line switch plunger (not shown) is attached to the plunger arm 19 which is controlled by a magnet. 15 having the line winding '15, a pull-in winding 10 and a bridgecut-otf winding 17. The magneticl circuit of the winding 15"L is separate and distinct from 'the magnetic. circuit of the wind-ings 16 and 17. The winding 15a controls the armature 18, the winding 1G controls the plunge'` -19 and also the hridge-eut-ott1 armature 20, while the winding 17 is streng enough' to only operate the said bridgecut oil armature 20. The various armatures allotted to this magnet 15 control the springs 21, 22, 23, 24 and 25, as. will hereinafter more fully appear. The line. switch is also provided with ten sets of bank terminals each comprising eight springs as follows: 26 and 27, 2S and 2S), 30 and 31, and 32 and 33. The master switch E comprises the usual plunger guide shaft (not shown), which is connected wit-h tire shaft 34 in such a manner that a rotary motion of the lattercoinmuncates an oscillatory motion to the guide shaft, a gear wheel a cani wheel `36 through the n'lcdium of which the operation of the master Iswitch is timed, the niotor relay 3 motor magnet. 38, open main relay 211) and a couple of auxiliary relays 40 and 41j 'lhe selector I comprises the line relay net 44, the release magnet 45, private niagnt 46, private magnet relay 47 and the release relay 48. As shown, the switch l" is also )royided with the usual side switch which,

51. and 52. The two-nay trunk ll has ex clusively allotted to it a trunk relay 5?, the line switch I which is a slight infaliication of the. line switch l) as far as the circuits are concerned (the mechanical operations ot' the two switches D and l heilig the saine). the line switch Movhich is a duplicate ot' the line switch I, and the trunk relay 5l which is a duplicate ot the. relay 5?. 'l`he selector L and the 'selector' 11" are the same as theselccttir l?. the line relay vertical magnet 56, rotary magnet 57, the release relay 58, the release l The connector' K comprises 1,

magnet 59, the ringer relay G0, back-bridge relay 163, private magnet relay (32, private magnet G3 and the locking relay G4. 'In addition there is provided in each exchange a busy-signal device N for supplying all busysignaling current to the exchange, and a signalling current to the exchange, and a ringer generator (l for supplying all ringing current. It is obv-ions, however, that one machine N and one machine may be made to furnish all necessary' current from these sources.

In addition to the foregoing general description of the system and apparatus and of the inode of operation. the system will no'wY be further described by explaining in detail each step taken by a calling subscriber in establishing connection with a desired subscriber and in disconnecting therefrom. For example, the subscriber C (Fig. 1), in establishing connection with the subscriber J (Fig. 3) whose number, it will be assumed., is 2120, proceeds by removing his receiver 4, thereby permitting the switchhook 5 to rise, with the result that the ringer ti is disconnected from across the. line, and the circuit closed through the transmitter 2, primary winding 65 of the induction-coil 3,

i and the impulse springs 10 and 9. This circuit is closed by the engagement of the springs 66 and 67. As soon as this circuit is closed the line winding 15i of the line switch D is energized in series with the auxiliary relay 40. The energizing,Y circuit, it will be seen. extends from ground (if at the line switch D through the springs 24 and 23 to the line conductor 13, thence through the phone to the line conductor 12 and back to the line switch D, then through the springs 22 and 21, winding 15u and coil 40, thence through said coil and thrt-iugltftfhe springs 68 and G9, and through the open main relaysprings 70 and 71 to the batterylead 72, thence through battery B to ground G. The \\'inf.ling 15", upon energizing, presses the springs 25 and 24 into Contact thi'bugh the medium of the armature 18, thereby energizing the pull-in winding 10. It will be seen that the energizhig circuit of the pull-in winding 1() is openat two points, namely between the springs 25 and 24 and between the auxiliary relay Springs 73 and 74; but since the windings 15a and 4() are energiaed in series, both of these points are closed at the. saine time. The flow of current is as follows: from ground G2 through the springs 24 and 25 and pull-in winding 16,' through the springs 73, 75 and 74, through the open main relay springsV 70 and 71 to the battery lead 72. When t-he auxiliary relay 40 energzes, not only is the circuit for "the pull-in magnet 1G closed at this point, *huts the energizing circuit for the relay 41 liii closed at the same time. Said relay, upon energizin g, opensl the circuit of tlie2rela'y 40,

which thereupon denergizes and thereby opens the energizing'circuit of the pull-in magnet 16. The time during which the -energizing circuit of the pull-1n magnet 16 is maintained is controlled by the action of the relays 41 and 40. In order that the` controlling action of the relays 40 and 41 may be insured these relays are, as indicated, loaded and made slow-acting. When the pull-in winding 1G energizes, the plunger is driven into the bank, and the armature 20 is, at the same time, so depressed that the springs 21 and 23 are separated from the springs 22 and 24, respectively. It will be seen that as soon as the springs 23 and 24 and the springs 21 and 22 separate, the energizing circuit for the winding 15a and also for the coil 40 is broken, so that thesev relays have no opportunity to renergize when the energizing circuit of the winding 15l and the relay 40 is again completed by the denergizing of the auxiliary relay 41. As previously stated,

there are ten trunk-lines running from the bank of the line switch D, only one of which is shown and which terminates in the selector F. For each one of these trunk-lines the master switch bank E is supplied with a corresponding contact. As shown in'Fig. 1, the trunk terminating in the select-or F has allotted -to it the master switch bank` contact 75. In the course of the description this trunk will be spoken of as the first trunk, inasmuch as the first contact 75 has been allotted .to it. The next trunk would, of course, have allotted to itthe contact 76 and would be spoken of as the second trunk, and so on, While the trunk to which the contact 77 is allotted will be spoken of as the tenth trunk. The purpose of the master switch E, it will be understood, is to maintain all plungers thatare kin locked engagement with the plunger shaft opposite the next idle trunk-line.

In this description it is assumed that the first trunlcline is the one that is idle atI the time that the subscriber Cf removes his receiver to malte hisI call. ln that casey the master switch wiper 78 is resting in engagement with the contact ,75, thereby maintaining the line. switch bank spring 3() in engagement. with the motor relay 37. W hen the plunger operates, as described, due to the energizing action of the winding 16, the line switch'bank springs (as sho-wn in Fig. 1) are brought into contact in sets as followsz2t and 27, 28 and 29. 30 and 31, and 32 and 33. By the closure or connection of the springs 26 and 27 on the negative side of thel line, and oi' the springsl 32 :unl

33 on the positive side of the line, the calling line is extended to the selector switch F. The instant that this circuit is completed to the selectorrF the line rela)v l2 energizes from ground (i3 through the winding 79 of said relay, through the telephone by way of the positive line conductor 13, thence through t-he'telephone to the negative line conductor v12, then through the second winding 81 ofV the selector line relay 42 to the battery lead 72, and through battery B to ground G. As soon as' the relayA 42 energizes, the spring 82 is separated fromvthe spring 83 and carried into contact with the spring 84, whereby the slowacting releaseK relay 48 is energized. The energizing current for this coil 48 flows from ground G* through the said springs 82 and 84 and through the coil 48 to the battery lead 72. As soon as the relay 48 operates, the springs 85 and 86 are brought into contact, and

Asince the side switch wiper 52 is in kfirst po- 17 of the olding the sition the bridge-cutoft` windin line switch D is energized for plunger in operative position. This energizing circuit, it will be seen, extends from ground G5 through the side switch Wiper 52springs 85 and 86, trunk-release conductor 87, through the bank springs 29 and 28, and through the bridge-cutpI Winding 17 to the battery lead 72. The closure of contact between the line switch bank springs 30 and 31 establishes a negative guarding potential at the master switch bank contact 75 through the resistance coil 88 for driving the master switch from opposite the trunk-line leading to the switch F, and for preventingy the master switch E .from again stopping on the contact.75 and thereby preventing any subscriber from tripping in on the trunk leading to the selector F until the trunk running to said switch is made idle. It will be seen that as soon as this guarding potential is set up a circuit is established .through the motor relay 37, since the master switch wiper 78 is resting on the contact 75 when the line switch bank springs 30,. and 31 close. This energizing circuit, it will be seen,.extends from ground i through the said relay 37, through the master switch bank common segment 89, master switch Wiper 78, contact 75, through the line switch bank springs 30 and 31, then through the resistance coil 88 tothe battery lead 72. The relay 37, upon energizing, closes the springs 90 and 91 in Contact, whereby an energizing circuit is closed for the magnets 39 and 38 which are connected in multiple` As soon as this circuit is closed the motor magnet 3 8 begins` to operate, advancing .the ratchet wheel 34 and the cam 36.'v 1t will be seen that the Inotor magnet 38 is provided with interrupt-ersprings 92 and 93,l so that Aits armature 94 `will' continue lo vibrate as long as the circuit is maintained closed at the springs 90 and 91. It lshould be explained that the teeth on the ratchet 35 are Vvery close together., and it re quires a number of operations of the magnet 38 to advance the master switch wiper '.78 i

from the contact 7 5 to the Contact. 73. Yflowis obvious that 'as-.long as -the springs 90 and 95 and 96 in contact. These spi-ings remain.

incontact until the next tooth on the cani ywheel 36 'separates the spring 95 from the spring 96, and by that time the wiper 78 has a vanced into engagement with the contact 76. Of course, if the'contact 76 is also busy the master switch will not stop o-n this Contact, but will pass on to the next, and so on. It is obvious that should the contact 76 be busy the usual guarding potential will be f und there by the wiper 78, and the motor relay 47 will, therefore, energize and repeat the operation already described. lt-

91, Vor the springs 95 and 96, are in contact the open main relay 39 remains energized, and it is also obvious that as long as this relay is energized no line switchis able to trip, since the circuits ofv all line windings 15l are open at this point. After the .calling subscriber has removed his receiver and thus obtained connection with the selector i switch F, as explained, he then operates his dial for sending in the impulses for tlie thousands digit of the number 2120. Iii so doijng he advances the impulse wheel 7 sufto second position, and more particularlyl when the side switch wiper 50 engages the contact point 104, theenergizing circuit for. tl'e rotary magnet 44 is closed. lThe rotary magnet. upon energizing, rotates the shaft om` step. thereby 'carrying the wipers 99, 100 and 101 into engagement with the first trunk-line which, in this` case, it is assumed is the trunk-line ll. (lf course, if thisv trunk-line is busy the selector will not stop on the first trunk-line, but will automatically rotate until it finds an idle trunk-line' iii the usual'nianner-that. is, 'the private wiper 101, upon finding the grounded contact point, ietnei'gizes the privatemagnct 46, whereby thelside switch is locked in sec-Av ond ptsitioii as ylong as the said private wiper continues to find such groundedcontacts. In the case assumed, however,namely that the first trunk-line Il isidle, the private. magnet` 46 does not renergize; b ut the ro,- tary magnet,l upon operating, not only rotates the shaft and wipers-as described,`l,t1t

` also operates the armature of the private magnet and 'trips the side switch t0. thirdy position. thereby breaking thel energizing circuit for the rotary magnet 44 and extending the calling line into connection with the l trunk-line ll through the side switchwipers:

Q 49 and 51. .is Shownr ficientlyso that on its return two of the i impulse teeth 8 willsuccessively engage the i impulse spring 10, separatin it twice from the main spring 9 and there y vcausing the `energizingcircuit, it will be seenrpasses `line relay 42 of the selector R to be ener- Each time that the said line 48 is energized and is slow-acting, thus= maintaining the springs 97 and 98 in contact, the vertical magnet 43 is energized twice by a flow ofcurrent from ground G* through the springs 82 and 83, though the t trunk conductor 116, thence through the line release relay springs 98 and 97 to the private magnet relay 47, thence through said l relay and through the vertical magnet 43 to theside switch wiper 5.0, thence to the -battery lead 72. By this operation the vertical magnet 43 raises the switch shaft and,there forel, the Wipers 99, 100 and 101 two steps.

It will be seen that the energizing circuit of magnet 43 passes through the private magnet relay 47. This relay447 energizes at the first impulse and, being slow-acting, re-A As soon as the subscribers line is.ext`ended into connection with the trunk-lineI H, the. trunk'relayfl (Fig. l) and the relays 106 and` v107 ofthe trunk switch M are energized in series. The

from ground Gr7 at the trunk relay 54 (Fig.y 3), thence through the` springs 1-09 and 108, conductor 110. springs 111 and 112 of lthe trunk switch M (Fig. 2;), to the trunk'conductor 113, through the winding 114 ofthe trunk relay 53 (l"ig..1), through the tele-4 phone and hack through the other winding 115 of the trunk relay -to the negative winding 106 of the trunk switch M, yand through the relay 107 to the batterylead 139 over a circuit similar t0 that traced for. tli'eiline yswitch D. The` result is thatjthe trunk relay 53 energizes, locking the release relay of the selector F and energizing the bridge-cut-ofl' relai,y of the trunk switch I, the trunk switch M is tripped, seizing the selector L, and making the trunk busy atthe Al exchange. lVhen the ytrunk relay .53 (Fig. 1) energizesit shiftsthc spring 117 into engagement with the spring 118, locking the release relay 48 of the selector F over a circuit extending 'from ground, Ga

through the selector'private wiper 101, se-

bank ntacts of the switches F1.

said springs 118 and 117, thence it extends over the conductor 120, through the bridgecut-ott relay 119 to the battery lead 72, As soon as the bridge-cut-oti winding 119 encrgizes. the bridge-cut-ott armature 121 is attracted. and the springs 122 and 123 are separated from the springs 122 and 123, as lshown. for disconnecting the switch I from across the trunk conductors.

lt `will be understood that. the trunk switch M operates exactly the Same as the line switch D (Fig. 1l), and that as soon as the vplunger operates, the bank springs shown in Fig. 2 are thrown into contact in the following order: 124 and'125, 126 and 127, 128 and 129, 130 and 13,1. Furthermore. it will be seen `that the selector LA acts exactly the same as the selector F as soon as the line is extended tothe said selector by, the. engagement of the trunk switch bank springs 124 and 125 onone side, and 130 and 131 on the other side-that is, the line relay 132 energizes, in turn energfzing the release relay 133, which then operates to lock the cut-oti` rela ,134 ofl the trunk switch M over the fo lowing circuit: from ground Gtfthroughthe side switch wiper 135, release relay springs 136 and 137,

trunk release conductor 138, trunk switchbank springs 12,7. and 126, bridge-cut-ol winding 134 to the battery .lead 139. It will be seen'that this ground G not only locks the bridge-cut0tt winding 134, as explained, but also supplies guarding potential over the conductor 140 to theprivate In this connection attention should be called to the fact that the guarding potential for the v switches F is supplied by the trunk relay 53 from ground G". It. should be understood that as soon as the trunk switoh M operates, the master switch E1 (which is the same as the master switch E, F ig. 1) also operates, exactly the same as the master switch E that is, the trunk leading to the selector L is vacated, and a guarding potent tial is maintained at the master switch bank contact. corresponding to this trunk, namely the contact 141, by the trunk switch M for maintaining the selector L busy. It is obvious that the magnets 142, 143, 144a and'145a 'of the master switch E1 are the same as the magnets 41, 39. 38 and 37.. respectively, of the master switch E. The subscriber is now ready to operate the dial for the hundreds digit 1, whereby the se lector L may be operated to establish connection with the connector K. It will be seen that the line relay 132 of theselector L is energized in series with tne windings of the trunk relay 53 (Figfl): hnt.- although the line relay 132 responds to the dial, the relay 53 docs not, it being a slow-acting re lay. Since the selector L operate/4s exactly the same as the selector' l" it responds to the `spouse to the action of the rela action of the dial in exactly the same manuel' as the selector F; and as Soon as the side switch passes to thirdV position ythe subscribers line is extended to the connector K over the heavy conductors, as shown.. It will be seen that as Soon as connection is established with the connector K the connector line relay energizes, thereby shiftingr the spring 144 onto the spring 145 and thus energizing the release relay 58 from ground G1u through the back-bridge relay springs 146" and 146, conductor 1,47, release relay 58 to the battery lead 139. As soon as the release relay 58 energizes, and more particularly as .soon as the springs 148 and 149 Vare closed in contact, the release relay 133 of the selector. L is locked from ground G through the side switchV wiper 150, springs 148 and 149, trunk-release conductor 151, side switch wiper 152 of rthe selector L, and through the release relay 133 to the battery lead 139. The subscriber is now ready to operate his dial for the tens-digit 2. In so doing he operates the line relay 55 twice, thus permitting the spring 144 t6 fall back onto the spring 153 twice, and in turn operating the vertical magnet 56 twice. It will be seen that this'energizing circuit for the vertical magnet 56 contains a private magnet relay 62, which is n slow-aeting relay exactly the same as the private magnet, relay 47 of the .selector F. This relay 62, upon energizing, in turn energizes the private magnet 63 by' pressing the Springs 154 and 155 into contact. This energizing circuit is, of course, broken when the impulses stop coming in` and therefore the private magnet 63 permits the side Switch to pass from first to second positi0n.-After the side switch vpasses to second position, and particularly as the side switch wiper 156 is then in engagement with the contact point 157. the subscriber is ready to operate his dial for the units digit 0. The line relay 55, of course, respondsten times, and as a result the rotary magnet 57 is elargized ten times in series with the slow'acting private magneti-clay 62.v By these two operations Vofthe dial it will be seen that the subscriber has raised the connector shaft one step and rotated it ten steps. thus carrying the connector wipers 153. 159 andlt() into engagement with the desired line.. As soon as the` private magnet 63 again denergizes, in ref 62, the connector side.- switch passes to tiird pos'rtion and thereby connects the calling and called subscribers ((asshown) byi the heavy conductors. Itwill be seen that Whenthe .side switchL rpasses` to third Yposition the side switch wiper 161 establishes.connection with@ the ground G, thle .j furnishing the guarding, potential a-'ttheprivatc wiper 166 v tor protecting the calledline. and also for Y energizing the bridge-cutotf windingl 162 of the called line. Also, when the side switch wiper 15G passes to third position an energiziiu' circuit. is established with the 'ringer rel-ay ti() in series with the ringer inlerrupter itil, whereby the called subscriber, as soon as connection is established with his line, is rung automatically. As soon as the called subscriber answers lie draws talking battery current through the back-bridge relay 1133, which relay then energizes and cuts off the ringing circuit by operating the springs 105 and 100; .After the subscribers are through talking, it` the. calling subscriber hangs up first he opens his` line circuit, at the telephone by separating the springs 66 and 6'?, and thereby permits the connector line relay 55 and the trunk relay 53 to deenergize. As soon as the trunk relay 53 de energizes, the energizing c1rcu1tl for the release relay 48 of the selector F is broken, with the result that the springs 85 and 86 are separated, while the springs 98 and 168 are closed in contact. rI`he separation of the springs 85 and 8G breaks the energizing circiiit of the cut-olf winding 17 of the line switch D, with the result that the plunger is released and the springs 26 and 27, 28 and Q9, 30 and 31, and 3Q and 33 are restored to normal, as well as the armature 20 which controls the springs 21 and Q3. By the engageinent of the springs 98 and 168 of the selector F the energizing circuit of the release magnet 45 is closed. -The circuit of this release magnet, when the shaft is in normal position, is open at a point between the contacts 16) and 170; but as soon as the shaft is raised one step these contacts close, and when the shaft 1s operated the only point where the release circuit is open is betweenthe springs 98 and 168. As soon as these springs come into contact, 'is stated, the switch is released. lt. should be stated, ot course, that the energizing circuit for the release magnet is, again broken when the shaft reachesI normal and separates the springsl 16S) and 170. \\"hcn the trunk relay 53 denergizes it not only produces the restoration of the selector Switch F and o1 the line switch l), but it also cuts oli the energizing circuit ol' the bridge-cut-otf winding 11.) of the trunk switch I, thereby permitting this switch I to be restored also. 'hcn the. connector line relay 55 deilner gizes, as stated, the release relay 58 also (leenergizes, thereby closing an energizing circuit for the release magnet. 59. which is in all respects siinila'r to that of the selector If.

rl`he connector switch shaft is, therefore, re-

stored, and the energizing circuit of the release magnet 5f) is breken as soon as the shaft reaches normal. Xot only dees the deciicigizing action ofY the release relay 58 release the connector, but by breaking the energizing circuit ot' the ielease relay 133 of the selector L this relay 133 dencrgizes,

y locking closing an energizing circuit forthe release magnet` 171. thereby releasing the selector4 switch L. The said relay 133 also breaks the the trunk switch M, thereby permitting this switch to be restored also. The connector switch `in releasing, as above explained, obviously breaks the energizing circuit of the britlge=cut0tt winding 102 of the called line, thus permitting the switch D to be also restored to normal.

In the foregoing description a. call over the trunk ll from the A exchangeto the A exchange hasl been fully considered. Y call in the reverse direction is obviously the saine, with the exception that in that case the calling line would be the line J, yfor example, which would operate the line switch D1 to establish connection witlrtlie` selector F1. The selector. F?, upon finding the trunk H, energizes the cut-oft' wind-ing 134 of the trunk switch M and operates the line switch I. It then connects the .trunk H with a selector switch similar to the se.

circuit of the cut-ott winding 134 of lector switch L, andfrom thence connection i may be made with a connector and With a called line. f

From the foregoing it Will -be seen that by my invention I provide a tWO-Way-trunk for use in conjunction with a two-wire ailgb'- toinatic telephone exchange system, -where-Jl t? by the two-Way trilnking is accomplishedy through the medium of complete metallic`l line circuits, and without grounding the' lines at the substations. Furthermore,- it( trunk having a non-numerical trunkingvv switch at each end thereof,' whereby either end of the trunk is extended in the direction of the callettsiibscriber by a non-niimerical trunking operation. -These twoway trunks which are equipped with nonniiinercal triinking switches at each end, are also equipped with masterswitches-y that is to say, there is at least .one masten, switch which is common to allof the trunks lat one end thereof, and another master switch which is common to all o't' the trunks at the other end thereof. In this way I also provide a two-wire systemfin which pro-vision is made for non-numerical trunking,r for the purpose of extending"connec` tion from trunk-lines to other' trunk-lines; and preferably this non-numerical triinkf ing occurs4 between the first and second selectors-that is to say, subsequent to the trunlcing operation in accordance with the first digit of the called number. biitrprior to the trunking operation for the'seond digit of the called number. ll'ith such arrangen'ient all et the numerical switches are common to the subscribers of the dif-- ferenti exchanges tor either.' lccal calls c1' l calls from one exchange to the other, `there being no numerical switches. that are inles lio

1,00 will be seen that I provide a twowirev f dividual to the twoway trunklines so that the same selectors are accessible either over the' two-Way trunks or over the one-way trunks of the same exchange, and nothing but non-numerical switches are allotted exclusively to the two-way trunks. Furthermore, with my improved two-way trunk arrangement the switches can be inspected and tested at the exchanges, by forcibly or manually causing a switch to seize one end of a two-way trunk-line without making the other end thereof busy.

In making tests or mechanical adjustments of switches it is often necessary or convenient to manually operate a switch to place its wipers in connection with a trunk line. From the explanation of the inode of operation of the system it is evident that if the selector F (Fig. 1) is thus manually operated to seize a trunk line there will he no telephone or other apparatus bridged across the line to close the circuit of the line relay of the trunk switch M at the distant exchange (Fig. 2), and thus noapparatusat the said exchange will be operated. Consequently, when the exchange inspector releases the switch that he was testing, as by forcibly or manually releasing the same, there is vthen no danger of the other end of the trunk-line being left in a busy condition, and consequently the switches can be .freely tested without danger when they are released of leaving the. two-way trunks in a busy or ofnormal condition. as "as heretofore the case with certain *kinds of apparatus.

My invention, it will be seen, relates to automatic telephone systems in which are used switches of the general character disclosed in United States Letters Iatent Nos. 815,176 and 81'5,321,gra'nted March 13. 19007 to Keith, Erickson and Erickson, the abovementioned British Patent No. 26,301 of 1906, the lVcste'r'n, Electrician of Chicago, Illinois, of January 25, 1908, and in the American Telephone Journal of New York, N. Y., of June 6, 1908. I

That l claim as my invention is:-

l. In a telephone system. a two-way trunklinc, a non-numerical trunking switch for each end of said line, and trunks. each switch adapted to automatically select idle' trunks.

2. In a telephone system` a two-way trunkline, means for seizing said line, a nonnumerical trunking switch for each end of said line, inst ruinentalities operative to make either end of the line busy when the other end is seized, and trunks, cach switch adapted to automatically select idle trunks.

il. In a telephone system, a two-way trunkline, a non-numerical trunking switch for cach end of said line, cach switch adapted to automaticany cxtcnfl a truulfingr connection from said line in the direction of the called .metallic line circuits. and

line, meansv foreizi-ng said line. a non-'f numerical trunki'hg, sivitch for each end of said line, instrumentalities operative to make both ends of-said trunk-line busy when either end thereof is seized, and trunks, each switch adapted to automatically select idle trunks.

5. 'In a telephone system, atwo-way trunkline, a. non-numerical trunking switch for each end of Said line, each switch adapted to automatically extend a trunking connec- -tion from said line in the direction 'of the called subscriber` numerical trunking switches for seizing either end of said trunkline, and instrumentalities. operative to render 'both ends of said trunk-line busy when either end thereof isl seized. 'l

G. In a telephone system, a set of two-way trunks, a (set of non-numerical trunking switches for the said trunks at one end thereof, a master switch for said set of trunking switches. another set. of non-numerical switches for said trunks at the other end thereof, and another master switch for .aid last-mentioned set of trunking switches.

7. In a telcphonevsystem'. a` trunk-line, another trunk-line, a nonniumerical trunking` switch for automatically connecting one trunk-line with the other, means for controlling said switch over a complete metallic line circuit, and automatic means for seizing either end of said first-mentioned trunkline.

8. In a telephone system, a trunk-line, an automatic switch for seizing one end of saidA trunk-line, another' trunk-line, a non-numerical trunkin'gr switch for automatically connecting the tirst trunk-line with the second trunk-line. means for successively controlling said switches over4 .complete `means' for automatically seizing. the other end of said firstmentioned trunk-line. l

9. In a telephone system. a two-way trunkline. means for automatically extending connection from either end thereofin the direc- 'tion of the called suhsciziher, automatic switches for seizing either end ofv said trunkline, and means for controlling said switches over complete metallic line circuits.

l0. In a vtelephone system,' a two-way trunk-line. automatic switches for extending connection from eitheend thereof in the ,dil-A rection of the called suScriber, other automatic switches for seizing either end of said truuk-linc, and means by which all of said switches are controlled over complete metalv lic line circuits.

11. Ina telephone system, a trunk-hne,-a-

. ate a ASwitch to .seize the trunk Cil first-Selector operative in accordance with thc first digit ot' the called nunlwr toi-cize one end ot' .said trunk-line. a sectnd-selector operative in accordance with the. .et-cond digit ol' the called numler to extend the cennectit n in the direction of thc called subscriher. a non-ninnerical trunkiirer 4witch t'f r i automatically evendtng ccnneetion trom the faid trunk-line to the second-Selectolz and meam4 whereby Isaid .-cleetcrs and switch are all controlled n er complete metallic line circuits.

1Q. ln a telt-phone fyi-tem. a twoway trunk, automatic witches for eelt/.ing either y end of said trunk. mean;-- tor making the endsl t of said trunk lut-y. and means for permitting an innpcetor to test and manually operuiihout making the other end thereof buey.

13. The combination. in a telephone system. of a two-way trunk line, a non-numerical trunlcing Switch for cach end of said line, a .switch provided with a member ha ving` one motion to find a group. and another t :notion to tintl the called line in any predetermined group, and mechaninu for controlling circuit over the said trunk line to control the said' niotionfs.

l-t. The conxhinatim. in a telephone tem. of a two-way trunk line. moana tot trunkmg.;-

seizing said line. a nmi-mnnerical I@witch for each end of said line. instrunn-ntalities operativey to make either end of'tho line busy when the other end is seized. a ,switch provided with a member having' one motion to find a group. and another motion to find the called line in any predetermined group. and mechanism for controllingr cirv cuit. over the said trtn'fIiline to control the said motions.

15. The combination, in a telephone System, of a two-nay trunk line, a non-numerical trunkingr Switch for each end of saidr line. each switch adapt-ed to automaticaliy extend a trunking connection from said liuc in the direction of the called subscriber. numerical trunking switchebl for seizing either ond ot said trunk line, instrumentalities operative to "render either end ot esaid trunk line busy when the other end is .St-ivd. a switch provided with a member baiting one motion to find a group. and anotherl motion to find the called line in any I lredetermined group, and mechanim for controlling.r circuit-over the Said trunk line to control the said motions.

iti. The combiinition, in a telephone sys;- tcm. ot" a two-way trunk line, meanS for seixing said line. a non-numerical trunking Switch for cach end ot said lint-.jnstrunientalitics operatire to maite both ends of said trunk iii-e haar when either end thcrcot i7; eeizcd. a .switch provided with a nicmlie-r.havinei one motion to tind a groten. r amont-te tin-i the called lino in [predetermined group. and mechanism for i controllingr circuit over the said trunk line i to control the said motions. l li'. The combination. in a telephone ,5r-- lltcai. of a two-way trunk lino. a non-nuY merical trunking switch for each end ol .-"lfl line. cach switch adapted to autoroutica|l extend a trunkingl connection l`rcm :said line in the direction ot' thtl called uhecriber. numerical trnnking switches t'or .eer/:ing either end ot said trunk line. in-.trumentalit'ies operative to render both end- 'of yaid trunk line busy when either end t'hereot' is seized. a switch provided with a member haring one motion todind a `group. and another motion to find thc called line in any 1u'edctm'mined group. and mechanism for controlling.r circuit over the naid l trunk line to control the said motions.

18. The comliination, in a telephone .system, ot' a set of two-Way trunks. a set of non-nunierical trunking switchen` Zor the 1said trunks at one'end thereof. a master ,switch for said set of trunkinrr switches. another set of non-nmnerical switcher; l'or `eaid trunksy at the other end thereof. an-

other master switch for Said last-mentioned t Set ot trnnkincr switches, a :switch provided i with a member having' one motion to "ind ia lsgroup. and another motion to find te l called line in any predetermined rjroup. and mechanism for controlling circuitV over the l l l l l l l l i s aid trunks to control the said motione.

` 1f. The combination. in a telephone l tem. ot a trunk' line. another trunk line. a l non-mnnerical trunking Switch for autolmatically connectingr one trunk line with the other. means for controlling said switch over a complete metallic line circuit, a i switch provided with a member having one motion to find a group, and another motion to find the called line in any predetermined group. and mechanism tor control- .lingr circuit over the said trunk lines to coutrol the said motions.

Q0. The combination. Ain a telephone. system. of a trunk line. an automatic switch for seizing said trunk line. another trunk line, a `non-rulmerical trunking switch for automatically connecting` the tirst trunk line with the second trunk line. mean.Q for successively controlling said switches over complete metallic line circuit a switch provided with a member haringl one motion to lind a group, and another motion to find the called line in any predetermined group. and mechanism for controlling' circuit over the said trunk lines to control the said motions.

i 2l,l yThey combination. in a telephone. system. of a two-way truuk line. means for automatically extention@- connect-ion from l either end thereof in the direction yof the sysi .trailed subscriber. automatic switches for i eeizing either end of said 4trunk line, Incoml list;

Error controlling said switches over complete clnding a two-way trunk line, a non-numerimetallic line circuits, a switch provided with a member having one motion to find a group, and another motion to find the called line in any predetermined group, and mechanism' t'or controlling circuit over the said trunk line to control the said motions.

Q2. The combination, in a telephone sys` teni, of a two-way trunk line, automatise switches for extending connection from either end thereof in the direction of the called subscriber, other automatic switches for seizing either end of said trunk line, means by which all of said switches are controlled over complete metallic line circuits, a switch provided with a member having one motion to find a group, and another'motion to'tind the called line in any predetermined group, and mechanism for controlling circuit over the said trunk line to control the said motions.

Q3. The combination, in a telephone system, of a trunk line, a first selector operative in accordance with the lirst digit of the called number to seize one end of said trunk line, a second selector operative in accordance with the second digit. of the called number to exteiid the connection in the direction of the called subscriber, a non-numerical trunking switch for automatically extending connection from the said trunk line to the second selector, means whereby said selectors and switch are all controlled over complete metallic line circuits, a switch provided with a member having one. motion to find a group, and another motion to find the called line in any predetermined group, and mechanism for controlling circuit over the said trunk line to control the said motions.

24. The combination, teni. of a two-way trunk, automatic switches for seizing either end of said trunk, means for making the ends of said trunk busy, means for permitting an inspector to test and manually operate a switch to seize the trunk without making the other end thereof busy. a switch provided with a member haring one motion to find a group, and another motion to tind the called line in any predetermined group, and mechanism for in a telephone sysvcontrollingr circuit over the said trunk to control the said motions. v

25. In a telephone system, subscribers lines, means for establishing a connection between two of said lines, said means incal automatic trunking switch for each end of said line, a central source or sources of electricity, and means for supplying current therefrom for talking purposes to substat-ions connected for conversation over said trunk line.

26. In a telephone system, subscribers lines, means for establishing a connection between two of said lines, said means 1ncluding a two-way trunk line, means for seizin said line, a non-numericat automatic' trunkmg switchefor each end of said line, instrumentalities operative to make either end of the line busy when the other end is seized, a central source or sources of electricity, and means 'for supplying current therefrom for talking purposes to substations connected for conversation over said trunk line.

27. In a telephone system, subscribers' lines, means for establishing a connection between two at' said lines, said means in cluding a two-way trunk line, a non-numerical trunking switchfor each end of said line, each switch adapted to automatically extend a 'trunking connection from said line in the direction of the called subscriber, numerical trunki'ng switches for seizing either end o1' Said trunk line, instrumentalities operative to render either end of said trunk line busy when the other end's seized, a central scarce or sources of electricity,-a'nd means for supA plying current therefrom for talking pur poses to substations connected for conversation over said trunk line.

28. In a telephone system, subscribers lines, means for establishing a connection between two of said lines, said means'including a two-way trunk line, meaus'for seizing said'line, a non-numerical automatic trunking switch for each end of said line. instrumentalities operative to make beth ends of said trunk line busy when either end thereof is seized, a central source or sourcesof electricity, and means for supplying current therefrom for talking purposes to substations connected for conversation over snif? trunk line.

29. In a telephone. system, subscribers" lines, means for establishing a connection between two of said lines, said means including a two-way trunk line, a non-numerical trunkin switch for cach end of said line. each switch adapted to automatically extend a trunking connection from said line in the direction of the called subscriber, numerical` trunking switches for seizing either end ofy ,said trunk line, instrumentalities operative to render both ends of said trunk line busy when either end thereof is seized, a central source or sources of electricity, and means for supplying current therefrom for talking purposes to substations connected for con versation oier said trunk line. l

30. In a telephone system, subscribers lines, means for establishing a connection between two of said lines, said means including a. set.- of two-way trunks, a -set of non-numerical trunking switches for the said trunks at one end thereof, a masten switch for said set. of trunking switches, another set of non-numer1cal switches for said trunks at the other end thereof, another Yze iastersvitch for said last-mentioned set of runkin swiches. a central source or ources of electrieit v, and means for supplying current therefrom tor talking purposes to sub- `stitif\=rs crnnef'ted t'er cmircrsation over aid trunlt's.

3l. ln a telephone system, Subscribers lines, means vtor establishing a connection between two ot said lines, said means including a truuk line. another trunk line, a nonnumerical trunlting lswitch for automatically connecting one trunk line with the other, means `for controlling said switch over a complete metallic line` circuit, a. central source or sources ot' electricity, and means for supplying current thercfromfor talking purposes to substations connected for conversation over said trunk lines.

32. ln a tolei hone system, subscribers lines, means for establisl'iing a connection between tuo o? said lines, said means including a trunk lintxan automatic switch for ser/:ing said trunk line, another trunk line, a noirnumerical' trunking switch for automatic-all) connecting the first trunk. line with the second trunk line, means for successively controlling said switches over complete metallic line circuits, la central source or sources of electricity, and means for supplying current therefrom for talking purposes to substations connected for conversation over said trunk lines.

33.111 a telephone system, subscribers lines, n'ieans for establishing a connection between two of said lines, said means including a two-Way trunkI line, means for automatically extending connection from either end thereof in the direction of the called sulfiscriber. automatic switches for seizing either end of said trunk line, meansfor controlling said switches over completo metallic liuc circuits, a central source or sources of electricity, and means for supplying current therefrom vfor talking purposesto sulistations connected for conversation over said truuk line.

IM. ln a telephone system, ,subscribers7 lines, means for establishing a connection between two of said lines, said means including a twoavay trunk line, automatic stitches tor extending connect-ion from valli-i subscriber, other automatic switches tor `rizing either end of said trunk line,

ns bv which all at said switches are coneil over complete metallic line circuits,

nryl`t't'..

a contri-.i source or sources of electricity, and means lor supplii'ing current therefrom for tallexugf` purposes to sul'istations connected for conversation over said trunk line..

Tlf. ln a telephone system, sdbscribens lines` means i'oi establishingh connection between two oi" laid lines, said infuus inY cluding a trunk line, a tirstselector opera- L orner end thereot intthe direction of the..

tive in accordance with the first digit of the called number to seize one end-ot said trunk line. a second sel-rotor operative in accord ance with the second digitl ol` the called number to extend the connection in the direction ot' the called subscriber. a nou-numerical trunking switch lor aulomaticalliv extending connection from the said trunk line to the second selector. means whereby said selectors and switch are all controlled over complete, metallic line circuits. a central source or sources ot' electricity, and means for supplying current therefrom for talking purposes to snbstations connected for conversation over said trunk line.

3G. In a telephone system, subscribers lines` means for establishing` a connection between two of said lines. said means including a two-way trunk` automatic switches for seizing either end of said trunk, means for making the ends of said trunk busy, means for permitting an inspector tov test and manually operate a switch to seize an end ot' the trunk without making the other end thereof busy, a central source or sources of electricity, and means for supplying current therefrom for talking purposes to substations connected for conversation over said trunk line.

B7. In a telephone system, a two-way trunk, an automatic switch for including said trunk in a calling connection in one direction, another automatic switch for including said trunk in a calling connection in the other direction, means including an automatic switch controllable over the two sides of the trunk line in series for completing the call in one direction, and means including another automatic switch cont-rollable over the two sides of the trunk line in series for completing the callin the other direction.

38. In a telephone system, a two-way. trunk line, an automatic switch for extend ing connection from one end of said trunk line, another automatic switch vfor extend ing connection from the other end of said trunk line, and` means for controlling each switch over the two sides of the trunk line in series.

2li). ln a telephone system, a twowvay trunk line, automatic mans for including said trunk line in a calling connection in one direction, automatic means for including said truuk line in a calling connection in the ether direction, subscribers7 lines, an automatic switch controllal'ile over said trunk. lin and the two sides of a subscribefs i line in series to extelld the all in one direc' tion, and :mother automatic switch eontrol lable over the trunlt line and the two sides ol a subscribcns line in `series to extend thc call in the other direction.

l0. ln a telephone system, a twowvay trunk, means including autoiiiatic switches Signed by me at- Chicago, Cook county, for automatically trunking in opposite di- Illinois, this 2nd day of July, 1908.

rections ove!l Said trunk line, and means for EDWARD D. FAES. controlling said :z utomatic switches over W'itnesses: the two sldes of said two-way trunk line. in J. NORBY,

series in either direction. ALBERT J. SAUsEn. 

